It's just not possible for us to have both at the same time, writes the CND's Kate Hudson.

As debate continues about the replacement of the Trident nuclear weapons system, many just assume that the United States automatically supports a new generation of British nuclear weapons – or even that they may not "let us" disarm. Those backing the retention and replacement of Britain’s nuclear arsenal often cite our obligations as part of NATO – a US-led nuclear alliance – and of our commitment to our allies in "an uncertain world". Indeed some even see nuclear cooperation with the US as the keystone in our "special relationship".

So it was interesting to read the following passage in the International Herald Tribune last week – "NATO at a turning point" (12 April) – under the heading "Sharing Capabilities":

As for Britain, Prime Minister David Cameron is insisting on keeping a nuclear deterrent on a new generation of submarines, even as U.S. officials are pushing London to consider abandoning the idea. As one U.S. official said privately, "They can’t afford Trident, and they need to confront the choice: either they can be a nuclear power and nothing else or a real military partner."

As the article clearly conveys, there are many in high places that would prefer Britain to be a well-equipped and viable conventional military force, capable of twenty-first century interventions and keeping up the European end of NATO military capacity. This lays bare one of the main arguments – whether implicit or explicit – put forward by those in favour of Trident replacement: that while times may be hard economically, maintaining a nuclear arsenal is the strong choice for defence policy. So it’s interesting to note that allies may see it as making us a bit of a military lame duck.

In fact, such a view is increasingly widespread here, as well as in the US, given the drastic reductions in personnel and capabilities as a result of cuts to the Ministry of Defence (MoD).

In the first instance, no-one should be in any doubt about the impact of Trident spending on UK defence equipment budgets.

The Royal United Services Institute (RUSI) has said that by the early 2020s, 'submarine and deterrent spending is set to account for around 35% of the total core procurement budget'. And by 2017, cuts to defence personnel will see regular troops reduced from 102,000 to 82,000 – with increasing reliance on reservists.

We are now starting to see previously pro-Trident news outlets such as London's Evening Standard and the Telegraph raising concerns about the government’s approach to defence priorities. The Evening Standard has written two excellent editorials on the question of Trident and defence spending, here and here, stating:

'Defence must take its share of cuts and choices must be made. Something has to give: it is worth asking again whether renewing the Trident nuclear missile system, on which design work alone will cost £350 million, is as good a use of defence funds as more boots on the ground. Given our present challenges, the answer must be no.'

While many are still right to put forward the moral and humanitarian arguments against nuclear weapons, they are increasingly joined by those who see the strength in the economic and strategic arguments against Trident. These are people with serious concerns about the thinking behind the government’s defence spending and security strategy. And of course they’re right that the costs will be astronomical and devastating.

The MoD puts the build cost of the "Successor" submarines alone at £20-25bn, which, given its track record of delivering major projects around 40 per cent over budget, might be more accurately predicted as £28-35bn. The maintenance costs will be £3bn per annum (not factoring in inflation) for 30-40 years according to former Minister for the Armed Forces Sir Nick Harvey MP. Then there’s the estimated £25bn decommissioning cost.

£100bn is now a considerable underestimation of Trident replacement costs. It is clear it will be more.

But even without the grim economics, Trident replacement seems at odds with both government analysis – the National Security Strategy downgraded the threat of state-on-state nuclear attack – and with the ability to fulfil government policy. As the Standard rightly points out:

The Foreign Secretary talks tough about North Africa and David Cameron regards Libya as one of his foreign policy successes. Yet they must know that interventions like that in Libya, or a British version of France’s exploits in Mali, would be impossible with drastic reductions in troop numbers.

And this is precisely what is being called into question in the US administration. What use is an ally which becomes incapable of action through a dearth of personnel and equipment? How would Britain’s nuclear weapons play any useful role in US operations?

This dilemma should be ringing alarm bells for Labour, whose shadow Defence Minister Jim Murphy MP recently outlined his vision of a flexible, dynamic, military with "adaptable units" to head off emerging security threats around the world. Labour needs to understand that it will not be able to afford both that and Trident.

The debate on Trident will continue, to the general election and beyond. But those who still think we are well-served by nuclear weapons would do well to heed the view of former Conservative Defence Secretary Michael Portillo: Trident, he says, is completely past its sell-by date and a tremendous waste of money. I can’t say fairer than that.